Boundary Layer Control with Injection and Suction Through a

Porous WallBy Crisen McKenzie

Why Control Boundary Layer

• Preventing flow separation

• Controlling flow turbulence

• Heat transfer

• Increasing/Decreasing drag

Suction of the Boundary Layer

• Decreases thickness of boundary layer

• Increases heat transfer from body to fluid

• Delays flow separation

• Allows for less turbulent flow

• Decreases maximum velocity downstream of flow

Blowing Into Boundary Layer

• Increases thickness of boundary layer

• Decreases heat transfer

• Allows for more turbulent flow

• Flow separation occurs sooner

• Greater maximum velocity of downstream to the flow

ANALYSIS

Fluent

• 2D Pipe flow with Suction/Injection Pipes located normal to fluid flow

• Three conditions– Normal– Suction– Injection

Flow Control Apparatus

1

1. Inlet 2. Outlet 3. Suction Pipes

2

3

0.4 m

Regular Pipe flow

• Regular Poiseuille flow

• Inlet Pressure: 10 kPa

• Outlet Pressure: ambient

Regular Mainstream Flow w/ No Outer Disturbances

Boundary Layer Thickness

Suction Boundary Conditions

• Regular poiseuille flow

• Inlet pressure: 10 kPa

• Outlet pressure: ambient

• Suction pipe pressure: -1kPa

Normal vs. Suction

Boundary Layer

Thickness

Velocity(m/s)

Boundary Layer

Thickness

Increased velocity close to wall

Velocity(m/s)

Injection Boundary Conditions

• Regular poiseuille flow

• Inlet pressure: 10 kPa

• Outlet pressure: ambient

• Injection pipe pressure: 1 kPa

Normal vs. Injection

Boundary Layer

Thickness

Velocity(m/s)

Boundary Layer

Thickness

Decreased velocity close to wall

Velocity(m/s)

Velocity Graphs

Injection Suction

Cross-sectional View of Velocity Profile 1 m Down Pipe

Velocity Profile (Normal/Suction/Injection)

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0 20 40 60 80 100 120 140

Velocity (m/s)

y (

m) Suction

Normal

Injection

Cross-sectional View of Velocity Profile 1 m Down Pipe

Velocity Profile (Normal/Suction/Injection)

-0.21

-0.2

-0.19

-0.18

-0.17

-0.16

-0.15

-0.14

-0.13

100 105 110 115 120 125 130 135

Velocity (m/s)

y (

m) Suction

Normal

Injection

Tube Wall

Turbulence Boundary Layer

SuctionInjection

Cross-Sectional View of Turbulence 1 m Down Pipe

Turbulence Intesity Profile

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 2 4 6 8 10

Turbulence Intensity

y (m

) Suction

Blowing

Normal

Cross-Sectional View of Turbulence 1 m Down Pipe

Turbulence Intesity Profile

0.1

0.2

2 2.5 3 3.5 4

Turbulence Intensity

y (m

)

Suction

Blowing

Normal

Tube Wall

Heat Transfer

• Lower skin friction Cf means lower heat transfer

mwavphw

fh

TTucCq

CC

2

1

Heat Transfer Graph

Injection Suction

Tw = 100 KT∞ = 300 K

Applications

• Preventing flow separation on wing.

• Decreasing parasitic drag on wing.

• Keeping turbine blades cool

• Decreasing boundary layer interference in wind tunnels.

• etc

Conclusion

• Controlling boundary layer can be very powerful when used.

• Used quite heavily in the aerospace environment.

• Both Suction and Blowing have their Pros and Cons and Used for different applications